1. Field of the Invention
The present invention relates to the technology field of radio frequency signal transmission and, particularly, to a transmission circuit for radio frequency signals and a method for transmitting radio frequency signals.
2. Description of the Prior Art
In current magnetic resonance imaging systems, a transmitting link of radio frequency signals for a body coil is shown in FIG. 1. Referring to FIG. 1, the transmitting link primarily includes a radio frequency amplifier 101, a transmitting antenna shift switch 102, a power mixer 103, a transmitting antenna 104, and a power load 105. In which case, the main role of the power amplifier 101 is to amplify the radio frequency signals to be transmitted. The main role of the transmitting antenna shift switch 102 is to switch the output power of the radio frequency amplifier 101 to the power mixer 103 or the power load 105, namely, to transmit the output power of the radio frequency amplifier 101 to a radio frequency input port 11 of the power mixer 103, so as to further provide it to the transmitting antenna 104 for transmitting; or to transmit the output power of the radio frequency amplifier 101 to the power load 105, so as to calibrate the radio frequency amplifier 101 by measuring. The main role of the power mixer 103 is to mix the radio frequency signals that are supplied as inputs from the transmitting antenna shift switch 102, so as to form the two orthogonal radio frequency signals, and to output them to the transmitting antenna 104 via the radio frequency output ports 12 and 13. The transmitting antenna 104 is mainly used for transmitting (emitting) the two channels of the radio frequency signals supplied thereto as inputs.
When the power mixer 103 transmits the two channels of the orthogonal radio frequency signals to the antenna via the radio frequency output ports 12 and 13, since the radio frequency device does not match or the reflection coefficients of multiple input ports of the transmitting antenna 104 are not the same, it will produce therefore a certain amount of reflected power, and this part of the reflected power is emitted to the transmitting antenna shift switch 102 from the dummy load port 14 of the power mixer 103. It is then switched to the power load 105 by the transmitting antenna shift switch 102 and is consumed there to avoid being returned to the radio frequency amplifier 101, which may damage the radio frequency amplifier 101.
In the transmitting link shown in FIG. 1, the transmitting antenna shift switch 102 not only switches the power signals that are emitted from the radio frequency amplifier 101 to the power mixer 103 or the power load 105, but also outputs the reflected power outputted from the dummy load port 14 of the power mixer 103 to the power load 105. Such a transmitting antenna shift switch 102 has high operating requirements, so its structure is relatively complicated, thereby leading to a relatively complicated transmitting link as shown in FIG. 1.